1. Field of the Invention
The present invention relates to a musical tone control system for a grand-type piano, for use e.g. in a compound piano, such as an electronic piano or a silent piano.
2. Description of the Related Art
As a conventional musical tone control system, there has been known one disclosed in Japanese Patent No. 3538871. The musical tone control system includes shutters each integrally formed on a pivotally movable key, and first and second photointerrupters associated with the key. Each shutter extends downward from the key integrally formed therewith, and has an inverted L shape formed by a rectangular rear half part and a front half part extending forward from an upper portion of the rear half part. The shutter has a window formed in a lower portion of the rear half part. The first and second photointerrupters are each comprised of a pair of a light emitting element and a light receiving element accommodated in a case, and are disposed below the respective rear and front half parts of the shutter.
In a key-released state, the optical paths of the respective first and second photointerrupters are both open. When the key is depressed in this state, the lower end of the rear half part of the shutter reaches the first photointerrupter, whereby the optical path of the first photointerrupter is blocked. When the key further pivotally moves, the lower edge of the window in the rear half part of the shutter reaches the first photointerrupter, whereby the optical path of the first photointerrupter is opened again. When the key pivotally moves further downward, the optical path of the second photointerrupter is blocked by the front half part of the shutter, and then the upper edge of the window in the rear half part of the shutter reaches the first photointerrupter, whereby the optical path of the first photointerrupter is blocked again. When the key is released in this state, the optical paths of the respective first and second photointerrupters are opened and blocked in the reverse order to the above.
The musical tone control system controls sounding of a musical tone based on first and second detection signals from the respective first and second photointerrupters. Specifically, a key depression speed between a time point when the optical path of the first photointerrupter is blocked and a time point when it is blocked again by the upper edge of the window after having been opened by the window is calculated, and the tone volume of the musical tone is set according to the calculated key depression speed. Then, when the optical path of the first photointerrupter is switched from the open state to the blocked state and the optical path of the second photointerrupter is also in the blocked state, sounding of the musical tone is started according to the set tone volume.
As described above, according to the conventional musical tone system, the tone volume of a musical tone and sounding timing for sounding the same are determined according to the blocked or open states of the optical paths of the first and second photointerrupters disposed at different heights. However, when the shutter and the two photointerrupters constructed as above are provided on a hammer side of a grand-type piano, the following problem occurs: While a space between keys and keybed is relatively large, a space above hammers, where pin blocks etc. are provided, is very small. For this reason, during pivotal motion of a hammer, the hammer shank of the hammer can come into contact with the cases accommodating the respective first and second photointerrupters. The problem can be avoided e.g. by disposing the cases at respective higher locations so as to prevent contact of the hammer shank therewith and increasing the length of the shutter. In this case, however, the shutter can come into contact with the pin block during pivotal motion of the hammer.